U.S. Pat. No. 4,591,667 (the '667 patent) discloses structure for a dome speaker that includes a dome-shaped diaphragm formed of a high rigidity material and having an outer periphery, a voice coil bobbin secured at a top end thereof to the outer periphery of the diaphragm, a voice coil mounted about the bobbin, and a variation means in the bobbin for varying the resonance conditions of the diaphragm. The variation means includes at least one cut-out portion provided at the top end of the bobbin and a sheet which closes the cut-out portion. Preferably, the diaphragm is made of a nitrified titanium alloy and the sheet is made from a material softer than the bobbin. The cut-out portion may have a width from about 7 to about 50 percent of the total circumferential length of the bobbin.
The '667 patent does not disclose having the voice coil 1 covering up any portion of any of the cut-out portions 2. As such, a dimension of the voice coil bobbin 1a in an intended direction of travel of the bobbin during operation of the speaker is greater than necessary.
U.S. Pat. No. 1,767,837 (particularly FIG. 7) discloses a speaker with a coil form 25 that includes a collar portion 46. The collar portion 46 has a flanged extension 43 which appears to be oriented at roughly a forty five degree angle relative to an intended direction of travel of the coil form 25 during operation of the speaker. Having the flanged extension 43 at such an angle causes a dimension of the coil form 25 in an intended direction of travel of the coil form 25 during operation of the speaker to be greater than necessary.